This invention relates to electronic devices and methods of making them, and more particularly to such devices and methods utilizing conductive organic materials.
Chemically-assembled electronic devices can serve as extensions of conventional circuits and devices. Such chemically-assembled devices include nanoscale or molecular scale electronic components. Molecular scale systems can offer distinct advantages in uniformity of structure and potentially lowered fabrication costs. Additionally, these molecular components can offer the advantage of ease of synthesis and the ability to create large varieties of structure by the use of facile chemical transformations.
The invention is based on the fabrication of molecular scale electronic devices, and the incorporation of such devices in useful circuits and components. The molecular scale electronic devices include an active reduction-oxidation center, which serves as a key element in the devices"" exhibition of large negative differential resistance (NDR), including room temperature NDR, large peak to valley ratios, and switchable conductive states. The molecular scale electronic devices can operate as memory devices by storing high or low conductivity states. The devices are writeable, readable, and erasable.
In one aspect, the invention provides an electronic device including at least two contacts, and a monolayer of conductive organic material forming a conductive path between the contacts. The conductive path includes at least one electron withdrawing group, which can be cyano, isocyano nitro, sulfonyl, xcex2-carboxyvinyl, sulfinyl, xcex2,xcex2-dicyanovinyl, halogenated alkyl, formyl, carboxyl, carbonyl, alkyloxycarbonyl and aryloxycarbonyl, 1-tetrazolyl, 5-chloro-1-tetrazolyl, carbamoyl, or sulfamoyl, preferably cyano, isocyano and nitro. The device can exhibit high and low conductivity states and can be made repeatedly switchable between the high and said low conductivity states. The low conductivity state can a current of less than about 100 pA or less than about 1 pA.
The high conductivity state can have a current at least about 200 times higher than the low conductivity state, preferably at least about 500 times higher than said low conductivity state, and more preferably at least about 1000 times higher than said low conductivity state. The electron withdrawing group can be bonded to a phenyl ring in the conductive path. At least one electron donating group can also be present in the conductive path.
The conductive path can include at least about 70% of its atoms being sp- or sp2-hybridized atoms and can include alternating ethynyl and aryl groups, or at least one phenyl-ethynyl linkage, with at least one of the phenyl groups substituted with an electron withdrawing group. The conductive path can further include binding groups which bind said conductive path to the contacts, for example, sulfur atoms, oxygen atoms, cyano, carboxy, diazonium salt, halide, isocyano, phosphine, or tellurium and selenium atoms. The conductive path can include biphenyl groups, or ethenyl groups.
In another aspect, the invention provides an electronic device including two contacts, with at least one contact being a palladium contact; and a self-assembled monolayer of a conductive organic molecule including a phenyl-ethynyl-substituted phenyl-ethynyl-phenyl linkage between the contacts, where the substituted phenyl includes at least one nitro group, and where the organic molecule is bonded to said palladium contact by at least one isocyano group on a terminal phenyl of said linkage.
In yet another aspect, the invention includes a memory circuit including an input, an output, a molecular electronic device, as described above, where one contact of the device bridges the input and output, and where another contact of the device is at a low potential, or grounded, and a comparator also bridging the input and output, where the comparator is in electrical communication with a reference voltage. A memory array can be made, including a plurality of these memory circuits arranged in an addressable array.
In yet a further aspect, the invention provides a static random access memory cell including at least a first and a second molecular electronic device as described above, where the first device has one of its contacts connected to a reference voltage, and another of its contacts connected to a node, and where the other device has one of its contacts connected to a low potential or ground, and another of its contacts connected to the node, and where the node is further connected to a low potential, or ground, and can also include a gain component.
The invention involves organic or organometallic molecules that store charge as a self-assembled nanoscale molecular device. The molecular devices form electronically programmable and erasable memory bits. These bits are compatible with conventional threshold levels. The memory bits can be configured into memory cells applicable to random access memory devices. The molecular devices in such memory cells have long bit retention times (over ten minutes).
As used herein, xe2x80x9cconjugationxe2x80x9d or xe2x80x9cconjugated groupsxe2x80x9d refers to an extended system of overlapping xcfx80 electrons on sp- and/or sp2-hybridized atoms. This results in overlapping xcfx80 electron density not only within each pair of sp- and/or sp2-hybridized atoms, but between them as well.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.